ary and defective veins - were observed. The supernumerary veins were considered as present only if an evident vein length could be detected, while slight thickenings were ignored. Most colonies did not show any teratology in wing venation, while a few ones provided several workers with abnormal wings; in these cases, some individuals showed two or more abnormalities. Spurs of various length protruding from the standard veins were the most frequent abnor-malities observed; among them an adventitious distal abscissa of the 2rs-m crossvein, a spur protruding from the 2nd abscissa of Rs vein into the 1stsubmarginal cell, and the extension of the Rs vein beyond the distal end of the marginal cell were rather common. In some cases two opposed spurs tended to join or a single vein branched, thus defining an open or even closed supernumerary cell. In defective veins the missing stretch varied considerably in length so that in a few cases two contiguous cells merged more or less completely. Wing venation teratology should be taken into account when using the wing venation pattern for a morphometric distinction of honey bee subspecies, and data from abnormal wings should not be acquired, especially if automated procedures are used.
KEY WORDS: forewing, honey bee, morphometry, supernumerary cells, wing veins.
INTRODUCTION
Honey bee (Apis mellifera L.) wing venation is quite distinctive, but can be easily referred to the overall pattern shown by the Apoidea (MICHENER, 2000), and more
generally by the Hymenoptera. Nomenclature and interpretation of wing veins and of vein bounded cells was much debated during the last two centuries; the relevant literature was recently reviewed by INTOPPAet al. (2000)
with special reference to Apoidea and a nomenclatural standardisation for bee wings was proposed. Nonetheless various other name systems are still in use to describe bee wing venation (AMIET, 1996; MICHENER, 2000; ENGEL, 2001) and that of ENGEL (2001) was followed in the present work (Fig. I).
Whichever the name given to veins and cells, their presence or absence and their shape are largely used to identify bee taxa at different levels. Particularly, forewing venation morphometry proved to be a useful tool in discriminating A. mellifera subspecies (DUPRAW, 1965;
RUTTNERet al., 1968, RUTTNER, 1988), strains (STRANGE
et al., 2008), and hybrids (RINDERERet al., 1990; NAZZI,
1992; MARLETTO et al., 1994; KELLER et al., 2014).
Lately, specific software was developed to speed or fully automate wing data acquisition and analysis under both the standard morphometry or the more innovative geometric morphometrics approach (FLORISet al., 2002;
MEIXNER & MEIXNER, 2004; TOFILSKI, 2004 and 2008;
– Received 6 October 2014 Accepted 24 October 2014 Published 10 December 2014 1Original scientific contribution presented and discussed at XV Meeting of A.I.S.A.S.P., Italian Section of I.U.S.S.I. (International Union for the Study of Social Insects); Reggio Emilia - Italy, 18-19 September 2014.
FRANCOYet al., 2008, GERULAet al., 2009; BOUGAet al.,
2011).
Honey bee wing venation shows a uniform and regular pattern in most of individual workers, but asymmetries between right and left wing (SMITHet al., 1997) or various
teratisms due to the presence of both supernumerary and defective veins are often observed (AKAHIRA& SAKAGAMI,
1959; BÄHRMANN R., 1963; TANet al., 2008; WĘGRZY
-NOWICZ, 2010; MAZEED, 2011). These anomalies are often
consi dered as the result of environmental and/or pathogenic troubles during wing development (SOOSE, 1954), but the presence of supernumerary veins is also interpreted as the reacquisition of ancestral traits thus providing an insight into honey bee evolutionary history (TANet al., 2008).
Since abnormal wing venation was occasionally observed also in Italian bee samples a more extensive investigation was carried out on worker bees from full size colonies and small nuclei in order to understand how widespread wing venation teratology is in A. mellifera and to gain some insight into the causes of this phenomenon.
MATERIALS AND METHODS
In the years 2006-2012, samples of 24 worker bees were taken from each of 66 full size colonies; a total of 1,584 worker bees were sampled. Most colonies were of Italian origin, but also two A. m. mellifera, three A. m. carnica, and one A. m. macedonica colonies were sampled. In 2012, 99 newly mated queens were obtained from 20 Italian queen breeders (five queens from each breeder except a single one who provided four queens only) for a survey on
the occurrence of honey bee queen anomalies and diseases; each queen was sent in a queen cage with some attending worker bees, taken from the queen mating nucleus; in all, 746 individuals were collected (37.3 ± 8.66 worker bees from each queen breeder). Worker bees sampled in a full size colony with a long established queen are reasonably daughters of the colony queen, while adult workers in a professional queen breeder mating nucleus are at any moment most likely daughters, not of the newly mated queen present in the nucleus, but of previous queens or came from other colonies present in the mating yard; therefore attending workers from queen cages can be regarded at best as a random sample of the breeder’s stock. From this point of view, nine of the breeders who provided the queens were on the official Italian register of queen breeders and their stocks were certified as pure A.
m. ligustica strains.
The right forewing of each worker bee was taken off the thorax, placed between glasses in a slide frame and scanned at 3,200 dpi with an Epson Perfection 4490 Photo scanner. The resulting images were enlarged and observed to trace wing venation anomalies; supernumerary veins were considered as present only if an evident vein length could be detected, while slight thickenings were ignored.
RESULTS
Most of the worker bees sampled from full size colonies showed a regular wing venation, but in 69 wings (4.36% of the total) various teratisms were observed (Tab. 1); no abnormal wings were found in 26 samples and a single abnormal wing was present in other 26 samples, while up to five abnormal wings were observed in the remaining samples. Some wings showed two or more teratisms so that a total of 85 wing venation abnormalities were observed. On the contrary, significantly more teratisms (χ2 = 74.100 with 1 degree of freedom; P = <0.001) were present in worker bees sampled from mating nuclei: 119 defective wings with a total of 130 wing venation abnormalities (Tab. 1). Moreover only the accompanying
workers from a single queen breeder showed no abnormal wings and no statistically significant difference in teratism occurrence was observed between the samples coming from facilities enrolled on the official Italian register of queen breeders and the others (χ2= 0.419 with 1 degree of freedom; P = 0.518).
Some wings showed the standard venation pattern, but an irregular course of one, most often the 1rs-m crossvein, or more veins was observed (Fig. II, a).
Spurs of various length protruding from the standard veins were the most frequent abnormalities observed. Among them, an adventitious distal abscissa of the 2rs-m crossvein (Fig. II, d), a spur protruding from the 2nd abscissa of the Rs vein into the 1st submarginal cell (Fig. II, c), and the extension of the Rs vein beyond the distal end of the marginal cell (Fig. II, b) were rather common.
In some cases two opposed spurs tended to join (Fig. II, e) or a single vein, most often the 1rs-m crossvein, branched, thus defining an open (Fig. III, a and b) or even closed (Fig. III, b) supernumerary cell.
The presence of defective veins was less common than the above mentioned abnormalities; in this instance, the missing stretch of the defective vein varied considerably in length so that in a few cases two contiguous cells merged more or less completely (Fig. IV, a, b, c, d, e).
DISCUSSION
The incidence of wing venation anomalies places the observed samples - taking into account the different approaches adopted by the authors who investigated such a teratology (AKAHIRA& SAKAGAMI, 1959; BÄHRMANNR.,
1963; TANet al., 2008; WĘGRZYNOWICZ et al., 2010;
MAZEED, 2011) - roughly at the same levels reported in the literature. Nevertheless the remarkable differences observed between worker bees from full size colonies and those from mating nuclei cannot be overlooked. Most probably worker bees reared in mating nuclei are more exposed to temperature fluctuations during metamo r -phosis than those reared in full size colonies (SOOSE,
Fig. I – Right mesothoracic Apis mellifera wing showing a regular venation with cells defined by longitudinal veins and transverse crossveins; the latters are denoted by two letters indicating which longitudinal veins they connect (anterior vein first, posterior second) and abbreviated by lowercase letters. 1: radial cell; 2: marginal cell; 3: 1stsubmarginal cell; 4: 2ndsubmarginal cell; 5: 3rdsubmarginal cell, 6: 1stmedial cell; 7: 2ndmedial cell; 8: 1stcubital cell; 9: 2ndcubital cell. A: anal vein; C: costal vein; Cu: cubital vein; M: medial (basal) vein; R: radial vein; Rs: radial sector; Sc: subcostal vein. The costal cell between C and Sc+M veins is so reduced to appear vir-tually absent.
1954), but also the possibility that queen breeder bee stocks showed some degree of inbreeding should be considered.
The adventitious distal abscissa of the 2rs-m crossvein so often observed is clearly the same wing venation anomaly reported by TANet al. (2008) and one could fully agree
with their conclusions on the phenomenon. Also the extension of the Rs vein beyond the distal end of the marginal cell could be regarded as the reappearance of a vein present in other bee genera (like Melitturga for instance) and lost by Apis during its evolution.
As observed long ago by ALPATOV (1929), various
teratisms affected the 1rs-m crossvein also in the examined samples thus suggesting that this vein is a rather instable one. On the other hand, the number of submarginal cells in the bee forewing is a widely used feature to distinguish among bee genera, though there is not agreement whether the 2nd
abscissa of Rs or the 1rs-m are lacking when only two submarginal cells are present and either case may be true for different species (TOFILSKI, 2011).
Since the wing venation pattern is widely used for the distinction of honey bee subspecies with a morphometric approach, any venation teratology observed in the worker bee sample used should not be overlooked because it could lead to a wrong attribution of the sample. In any case, data from abnormal wings should not be acquired and the whole sample should be prudentially discarded if two or more wings show any abnormality especially if automated procedures are used for data retrieving. Moreover worker bee samples should be obtained from full size colonies and not from small nuclei or from queen cages since these have proved to be more prone to show wing venation teratisms.
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Fig. II – Right mesothoracic Apis mellifera wings showing an irregular course of the 1rs-m crossvein (a) and several spurs protruding from various veins: abscissa of Rs beyond the distal end of the marginal cell (b); spur protruding from the 2ndabscissa of the Rs vein into the 1stsubmarginal cell (c); adventitious dis-tal abscissa of the 2rs-m crossvein (d); two spurs protruding from 1rs-m and 2rs-m crossveins, spurs which nearly meet dividing the 3rdsubmarginal cell into two separate cells (e).
Fig, III – Right mesothoracic Apis mellifera wings showing a forked 1rs-m crossvein: a) complete vein forming a closed supernumerary submarginal cell; b) incomplete, but forked vein forming an open super-numerary submarginal cell.
Fig. IV – Right mesothoracic Apis mellifera wings showing: a) incomplete 1rs-m crossvein causing a par-tial merging of 2ndand 3rdsubmarginal cells; b) incomplete 1m-cu crossvein causing a partial merging of 1stand 2ndmedial cells; c) M and d) Rs+M veins interrupted, e) 2ndabscissa of the Rs vein reduced to a spur so that 1stand 2ndsubmarginal cells merge; f) incomplete supernumerary vein dividing the 2nd medi-al cell; g) spur protruding from the Cu1 vein.
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